The effects of entrainment-mixing on the cloud droplet size distribution are examined in the Pi cloud chamber that creates a turbulent supersaturated environment for cloud formation. The experiments are conducted with a temperature-controlled flange to mimic the entrainment-mixing process. The entrainment zone is created at the center of the top surface of the chamber, allowing dry air of controlled temperature (Te) and flow rate (Qe) to flow into the mixing cloud region. Due to the large-scale circulation, the downwind region is directly affected by entrained dry air from the flange, whereas the upwind region is representative of the background conditions in the cloud chamber. Compared to the upwind and center regions, droplet concentration (Cn) and liquid water content (L) decrease in the downwind region, but the difference in the mean diameter of droplets (Dm) between the three regions is small. The shape of cloud droplet size distributions in the three regions is unchanged, to within statistical uncertainty, suggesting an inhomogeneous mixing. As Te and Qe of entrained air increase, Cn, L, and Dm of the whole cloud system decrease, which is consistent with a homogeneous mixing response. The apparent contradiction is understood as the cloud microphysical responses to entrainment and mixing differing on local and global scales: locally inhomogeneous and globally homogeneous. This study provides critical insights into distinct signatures of microphysical effects of the entrainment-mixing process needed to advance the parameterization of this process in the simulations and design future laboratory experiments.
Cloud microphysical response to entrainment and mixing is locally inhomogeneous and globally homogeneous: Evidence from the lab.
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